text:
What aircraft has the highest suggested landing speed?
Just out of vague curiosity, what aircraft has the highest recommended landing speed for an earth bound (atmospheric) craft?  And, btw, when I say "landing" I define it as thus:

Controlled
Powered (though if you want to note unpowered, feel free)
Safe, with the vehicle/aircraft fully recoverable
On a runway
On wheels or skids

I know there may be multiple answers, even with my trying to narrow it down, so feel free to list a few different scenarios.  I'm mostly wondering about planes that are in common usage though, both military and civilian (past and present)...  I'd have to think something like the SR-71 or MIG-25 would be very close to the top of the list, if not the top.

Concorde's landing speed was 300 km/h (http://www.britishairways.com/en-au/information/about-ba/history-and-heritage/celebrating-concorde), whereas the SR-71's was about 290 km/h (http://www.airliners.net/aviation-forums/military/read.main/29176/). If it counts, the Space Shuttle landed at 350 km/h.

I'm trying to avoid "unpowered" mainly because of the Space Shuttle actually.  I know that craft was coming in rather fast :).

@Hugh There, edited the question to deal with only "earth bound" craft... sorry.  I'm just not after the Space Shuttle on this one.

The Space Shuttle wasn't capable of leaving Earth orbit, so one could argue it was every bit as "Earthbound" as any other aircraft... ;-)

@dvnrrs by those standards, it was not able to leave ground at all: it had no fuel on board.

@Federico Not strictly true: it carried hypergolic fuel for its OMS rockets used to change orbits (enough for about 1,000 ft/sec total Δv), and of course RCS fuel for attitude control. But even with the SRBs and external tank, it was still not capable of leaving Earth orbit, hence "Earthbound" :) My point was that maybe "atmospheric" would be a better qualifier than "Earthbound" since the vast majority of our "spacecraft" (except interplanetary probes and the Apollo hardware) are still "Earthbound."

@dvnrrs, I was considering OMS rockets "negligible" to leave the surface. Also, I did the most basic of the mistakes: misinterpreted "Earth orbit". I agree on the atmospheric point.

Given the Shuttle's rather poor aerodynamics (slightly better than a streamlined rock), and the fact that the "flying" part accounts for only the last ~10 minutes of each trip, do we want to even consider it an aircraft?

@dvnrrs sigh Try and ask a bunch of engineers and enthusiasts a simple question........... ;)

@dvnrrs Also, since I just can't stand not being pedantic myself, if someone had taken the time to build a fuel tank that could be launched into orbit and attached to the Shuttle (which had ports for it) then the Shuttle could have easily left Earth Orbit, so there :p

@JayCarr If someone had taken the time to build a jet pack with appropriate guidance systems and harness, then pigs could easily fly... ;-) OK, I'm done, I promise!

@dvnrrs lol, you have captured the spirit of the discussion perfectly ;).

The Concorde benefits to some degree from the phenomenon of “vortex lift,” so it may have a lower landing speed than other aircraft of comparable size and wing loading...

Based on its fixed-wing hypersonic design and inordinately high wing loading, I would predict that the X-15 has the highest recommend landing speed of any earthbound aircraft, with a preliminary search seemingly bearing this hypothesis out. According to an ostensibly legitimate NASA source (link below), the X-15's normal landing speed was 200+mph (173.8kts=321.9kph),
http://www.nasa.gov/centers/armstrong/news/FactSheets/FS-052-DFRC.html
But if unofficial sources are to be believed, its actual landing speed was much higher, closer to 390kph=208kts (although these numbers are admittedly more dubious):

“According to an early edition of 'the Guinness book of world records' the X15 also holds the record for fastest landing speed at 242 mph compared with 210 mph for the space shuttle.”

http://area51specialprojects.com/x15.html
If only powered aircraft are open to consideration, then the F-104 Starfighter would have to be up there as well. It needed a blown-flap flow control system just to be sane during landing...

“To make landing speeds “reasonable,” The F-104 forced engine air through the wings to smooth the airflow and give more lift. With bleed air, the Zipper could land at the challenging but not extreme speed of 160 to 165 knots. If the air-bleed system was not working, landing speeds climbed to 240 knots.”

http://www.pacificaviationmuseum.org/pearl-harbor-blog/lockheed-f-104-starfighter
So, if mechanical failure scenarios are deemed admissible, then the F-104 without its crucial boundary layer control systems would be the clear winner for powered landing speed, weighing in at an absolutely terrifying 240 kts. Otherwise, it would appear that the X-15 (unofficially) reigns supreme.

NASA's 200mph was probably design speed, while the 240 was actual as used during missions.

And the XF-104 made a deadstick landing on at least one occasion.

More high speed lawndarts:
Presenting the F-102A Delta Dagger.

http://www.amazon.com/Convair-Dagger-Pilots-Flight-Operating/dp/1430310464 lists final approach speeds as high as 185 KIAS, with touchdown speed of 145 KIAS for the same fuel load.

And the B-58 Hustler
http://www.aviation-history.com/convair/b58.html says it had a touchdown speed of 165 KIAS. Which would lead to an approach speed even higher than that of the F-102.
http://wikimapia.org/7029449/Important-B-58-landing-approach-aid says it landed at "just under 200 knots", even higher then unless they mean approach speed rather than touchdown speed.
The XB-70
http://www.nasa.gov/centers/dryden/pdf/87774main_H-587.pdf mentions an approach speed of 200-210KIAS, with touchdown at 175-185KIAS.
And that for a lightly loaded prototype, the production machines would have been heavier...

So that may well be the top candidate for the job (excluding non-normal operations), if we exclude the X-15 and Space Shuttle which were gliders during their landing phase.

Concorde's landing speed was 300 km/h. Its high speed was due to its small wings, designed for supercruise, which required higher airspeeds to maintain lift during the approach. Possibly the XB-70 Valkyrie, being also a large supersonic aircraft, would have had higher landing speeds, but I can't find a reference for its landing speed.
The Space Shuttle regularly landed at 350-400 km/h under control, though without power.

Since in your comment you cite the Concorde and the SR-71 as well, it would be nice if you could include them also in the answer.

I'd have to concur.  My guess is the answer to this will end up looking somewhat like the "what's the fastest plane" question.  Which will hopefully satisfy my curiosity...

Sadly, even though your source is NASA, that press packet is inexplicably full of misinformation. It's true that very early missions targeted 185 knots (approximately 343 km/h), but after that it was actually faster. They used 195 knots for "light" and 205 knots for "heavy" orbiters (361-380 km/h). See the Shuttle Crew Operations Manual for more accurate information.

@BretCopeland I implicitly trust your information over its rivals because you correctly refer to the STS landing vehicle as the “orbiter.” Over the years I have had many a NASA colleague correct me after erringly referring to it as “The Space Shuttle. ”

@BrysonS. it is the space shuttle orbiter. Saying you can't call it the shuttle seems snobbish. I've heard NASA astronauts and engineers refer to it as the shuttle all the time.

I didn't say that my friends weren't snobbish ;-)

A 20-degree glideslope?  The SS orbiter really was a brick...

The USAF 101-B (ADC)did fly final approach at 175 plus fuel...it also had a 300 foot altimeter error subsonic at most landing altitudes! This was an all-weather interceptor! I will never forget landing at Kingsley fold, Klamath Falls, OR,at night, in a rain storm wth my rain clearing system inop!

The CF-101 Voodoo had a landing speed of 175 kts plus fuel weight over 3000 lbs over which it was 5 kts per 1000 lbs of fuel.  BTW crash landed one at 195 kts in Feb 82.


text:
What is the tablet/application being used in this 737?
In this video (marker 2:32), you can see that the captain has a tablet mounted to his left with some sort of application open in it. It looks like an iPad (though I could be wrong), but what I'm mostly wondering is what that application is he has open, and what it's being used for?

Just to make peoples lives as bit easier, here's a screen cap from 2:32:

I don't know enough to answer, but it's probably a company-specific "electronic flight bag" application, allowing him to access his pilot's log, the aircraft's maintenance log, loading/balance calculations for the flight, airport arrival/departure schedule, etc.

The screens on both electronic flight bags show airspeeds, which would indicate performance data. Specifically, the first officer has a speed card up.
I can't say for certain, but I think the pilot is using the iPad version of the Boeing Onboard Performance Tool. This application is used for weight and balance and performance calculations (which is especially appropriate, since they're flying a Boeing aircraft).

Definitely the Boeing Onboard Performance Tool. Here you can find an official Boeing impression of the screen which shows the letters ATM in the background. These are visible in the youtube video as well.

If you could include @DeltaLima's link in your answer as well, I think we can call this one complete :D.

According to this BBC News report, American Airlines uses an app called "FliteDeck" on a tablet computer, to avoid pilots having to carry multiple kilograms of documents with them. It says AA saves over a million dollars a year in fuel bills from not carrying all that paper around.  The app contains charts and things like that.
Other airlines use similar systems so that's probably what we're seeing in Air Vanuatu cockpit in the video.

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/

sort: votes


text:
How can investigators tell the difference between impact damage and explosion damage when investigating debris from a crash?
When reading this article on the debris they found from Flight MH370 they mention a lab in France that is supposed to be able to look at the debris (a flaperon), and figure out if the flight had exploded in mid-air or if it had broken up on impact with the ocean.
This has left me wondering, how would they do that?  How can the folks from that lab tell from an exterior control surface1 that the plane had exploded or broken up on impact?

1 Examples may include elevons, flaperons, elevators, ruddervators, basically anything that helps the plane maneuver and is exterior to the fuselage.

The short answer (to the question in your subject line) is that in an explosion the skin is blown outward, and in impact damage it's (usually) blown inward: In other words you can tell the direction of the force applied by which way the skin around a break/penetration is bent, if you recover the right bits of the aircraft.
The labs start with "Boom = Outie, Crash = Innie", and they can also look at burn patterns (on the paint or as changes in the heat treatment of the metal), chemical residue (if it hasn't all washed away or been contaminated), etc.
In addition to leaving chemical traces or heat-related damage explosions also tend to be physically "messy", so there's usually some physical evidence. Shrapnel punctures through control surfaces are a distinct possibility in an explosion (those punctures generally have a different characteristic than denting and tearing from impact with rocky ground, and again if you get lucky you might even find bits of shrapnel inside the punctured control surface).
The longer answer (to the rest of the question) is that sometimes you can't conclusively tell what happened, particularly from just a single piece of wreckage like a control surface.
In fact quoting from the story you linked there are three different (and valid) theories about what could have caused the damage seen on the particular piece of debris in question:

The rear damage could have been caused if the airliner had its flaperon down as it went into the ocean, some members of Exner's group wrote in a preliminary assessment after looking at photos and videos of the component.

Entirely plausible: Impacting water at speed could tear chunks out of the trailing edge of a flaperon. It could also break the control surface free of the rest of the wing.

But the lack of damage to the front makes it more likely the plane was in a high-speed, steep, spiral descent and the part fluttered until it broke off, the group said.

Also plausible: Aerodynamic flutter could break pieces of the flaperon off, or tear the entire control surface from the aircraft (in which case damage may be evident at the points where the flaperon attached to the rest of the wing)

The lack of damage to the front section "tells me that the component could still have likely been back in its original position inside the wing itself,"

Still plausible but a bit more exotic: The flaperon could have broken off post-impact (and the damage to the trailing edge could have occurred on impact, post-impact, or even pre-impact while the aircraft was still flying).

Note that a lot of what's being put forth in that article (and others) is speculation based on a few photos showing only part of the debris (so far I haven't seen any showing the "bottom" of the debris). A conclusive determination can only be made when the debris is recovered and examined in its entirety.
Attempting to draw conclusions without the full picture can lead to interesting results: The apple is perfect until you see the other side.

One minor quibble: in the case of a control surface, unless the explosion were actually inside the control surface, it wouldn't necessarily be blown outward. Even if the fuselage were blown up (a la Pan Am 103,) the wing wouldn't necessarily explode mid-air, but might instead crash into the ground mostly in-tact (at which point it might then explode, due to the impact energy being absorbed by literally several tons of kerosene.) Either a crash into the ground or an explosion exterior to the control surface could cause crumple damage to the control surface, though with different patterns.

@reirab Yes, but in the case of an explosion you'd (probably) have shrapnel damage or other telltale signs (burns) on nearby control surfaces, while impact with the ground will leave other telltale marks depending on exactly how the fragment in question impacted the surface (and what it landed on: Water and rocks obviously have different impact signatures). Post-impact fires further complicate matters, but those too usually leave evidence (the scorched ground around them) - that kind of context is critical in an investigation.

@voretaq7 why so much emphasis on the control surfaces? Typically an aircraft that suffered a bombing would have the bomb placed either in the cargo hold or the cabin, would investigators not be more focused on the fuselage skin itself as opposed to the control surfaces?

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
Why don't airliner winglets have consumer advertising on them?
I was looking over the wikipedia article for the 737NG when I came across this picture:

As you can see, the operator of the jet has written their companies web address on the winglet.  Which seems like a waste, I'm already on their airplane, there's no need to sell me, it's not so much an ad as a reminder at that point...
So, I couldn't help but think, when looking at it, that it would be somewhat clever if RedBull bought the rights to advertise on a 737NG and wrote something on that spot that said, "Redbull gives you winglets" (rimshot).
Sillines aside, there is a serious question here.  Generally speaking if there is a public surface that many many people will be forced to stare at for any length of time, then there is an advertisement there.  Bus stops, billboards, the sides of buildings, there are ads virtually everywhere.  Heck, commercial aviation equipment even has a few already with some of the jetways you see at airports:

There are tens of thousands of people who see winglets every day (and even more who see winglets in travel pictures, blogs, etc), so why aren't advertisers taking advantage of the space and, further, why aren't airlines trying to sell the space in order to increase revenue?
I'm wondering if perhaps there are regulations that might make this difficult?  A good advertising spot will change images and products fairly frequently.  On a winglet that would necessitate either a new paint job or, perhaps, a new vinyl wrap (like what is used in NASCAR.)  And I'm wondering if the regulations for commercial aircraft regarding how the winglets are painted would prohibit this sort of "quick switch" activity (are wraps even legal)?  Or perhaps there is a certification process for all new paint jobs that would make it so the amount spent to advertise would never match the increase in sales?
Or is it just that airlines have a sense of pride about their aircraft and respect their passengers enough to not bombard them with ads?  (...yeah, I doubt it's this last one as well ;-) ).

Edit:  I did mark this one for FAA Regulations, but I feel EASA regulations should be similar enough to give some insight as well, so if you want to answer with those regs feel free.

PLEEEEASE don't give them any ideas!

@JayCarr Its whether the airline choses to have their advertisement on the winglet like for example southwest on almost all their airplanes has a advertisement on the winglet and the winglet is the perfect place to put an advertisement on it instead of the rudder because some people don't even look at the airplane before they fly on it, so them sitting near the wing could sell them to fly on southwest airlines their next trip.

@Ethan, I agree, which is why I'm asking why they don't perhaps sell the space to other advertisers (like Red Bull or Coke), who might be willing to pay good money to have an add in that spot.

You may extend your question to other part of the aircraft that are visible to passenger, either from inside the aircraft (let's say seats, luggage compartements,...) or from the terminal (the whole painting, as for some city buses)

@JayCarr Its because other companies don't need to advertise on a winglet because they have commercials or billboard signs that do the advertising they don't need to waste their money on putting an ad on the winglet of an airplane. And everybody knows about coke and Red bull, so those companies prefer to advertise through commercials and on bill boards

@Ethan - They do, and those are certainly going to have more views.  But marketers are pretty much aaaalllways looking for other ways to get their brand out there.  The more often you see their logo, they figure, the more you think about their product, and the more likely you are to buy :).

@JayCarr It could happen in the future

@JayCarr Its probably because the airlines don't won't other companies advertisements on their airplane and they want more customers by advertising themselves instead of other brands

Why airlines don't put third-party ads on winglets
I would assume that a significant part of the answer is that it would look and feel cheap (i.e. not good for the airline's brand image.) They don't usually sell advertising elsewhere on their livery for much the same reason (though they do occasionally dedicate a livery to advertising some charity or some such thing, but that doesn't normally hurt their brand image.) On the other hand, putting the airline's brand image there can possibly help to improve it.
While you are already on the airline's flight, they'd be quite happy if you purchased more flights with them in the future and even more happy if you purchase the tickets directly from their website where they don't have to share the revenue with a travel agent. An additional benefit of mentioning the website is that many airlines now have on-board Wi-Fi and allow you to access their website from it even if you haven't paid for the Wi-Fi. As such, if they can get you thinking about their website and you happen to hop on it and book your next trip while cruising around at 30,000 feet, that's a win for them.
Finally, while they do already have you on board, they're well aware that lots of people post pictures taken while they were on a flight, especially pictures that include the wing (such as the one in the question.) Now your pictures are free (and usually positive) advertising for them.

Vinyl Wraps / Decals
As far as wraps are concerned, as far as I know, yes, they're legal and actually pretty common, even for the fuselage livery. My understanding is that lessors use them pretty frequently. They've also been used for temporary liveries like this one:

It appears that several companies exist for the sole purpose of making aircraft wraps. A quick search found the following:
AdGraphics
AircraftWraps
Plane Vinyl
It appears that 3M makes a lot of the materials used for the wraps.
I also found an FAA document on aircraft coatings that talks about how to apply vinyl decals to aircraft (along with how to paint aircraft, etc.) From page 18:

Vinyl Film Decals
  To apply vinyl film decals, separate the paper backing from the plastic film. Remove any paper backing adhering to the adhesive by rubbing the area gently with a clean cloth saturated with water. Remove small pieces of remaining paper with masking tape.

Place vinyl film, adhesive side up, on a clean porous
  surface, such as wood or blotter paper.
Apply recommended activator to the adhesive in firm,
  even strokes to the adhesive side of decal.
Position the decal in the proper location, while
  adhesive is still tacky, with only one edge contacting
  the prepared surface.
Work a roller across the decal with overlapping strokes
  until all air bubbles are removed.

This page from signindustry.com goes into more detail about how to apply vinyl decals to aircraft from a professional installer standpoint.

Do you know of anywhere that specifically states that wraps are okay?  I mean, the picture is kind of self evident, but I was kind of wondering about the rules regarding how they're applied and things such as that...  All the same, this basically answers the questions so, there you go.

@JayCarr Wonder what happens if the wrap starts to peel off mid flight. Would it shred or come off as one large piece. Would the debris get into the engines? Wrap and foul a control surface? Or is that too unlikely & the air flow would clear any debris instantly?

@JayCarr In a quick search, I haven't found the exact regs yet, but I did find several companies that make vinyl wraps for aircraft and an FAA document that talks about how to apply vinyl decals.

@JayCarr Answer updated to include some of the info I found on vinyl wraps/decals.

@curious_cat If applied properly I doubt they would come lose...  But I bet there are some surfaces you are not be allowed to attach them to just incase they do come lose.  Like the top of the wing, for example, since that would disrupt the airfoil.  Though I'm not sure if the winglet would count as part of that or not...  Since it isn't used to generate lift but rather to reduce the tip vortex.

@JayCarr At least some of the sites I linked earlier show them on at least part of the wing surface. Granted, those are light aircraft, not jets.

I doubt the space is worth very much. The interior side of the winglet is really only visible to people on the plane and even most people on the plane can't see it well. You're only advertising to people with window seats at or behind the wing, plus a few people in non-window seats close to the wing who can see the winglet while looking almost perpendicularly out of the plane. That's only a few tens of people per flight who can see the ad. Multiply that by a few round-trips per day per plane and your ad is only reaching a couplefew hundred people a day. Given the cost of applying the ad to the winglets, I doubt that's economically viable, when you consider that a billboard ad can be seen by thousands of people an hour and is much cheaper to produce.

I completely agree, if it was viable Ryanair would have done it already.

Plus, it gives your company a VERY cheap image. Some LCC wouldn't mind tho.

Before we see Winglet ads the Airlines ought to be putting ads inside on seat-backs n walls n bulkheads etc. More sq. feet, more visibility, less trouble to paint.

@curious_cat Some already do put some ads on the seat-backs, if you count the IFE systems.


text:
Do I need FAA permission to install tundra tires on a Piper PA-28 Cherokee 140?
I do a lot of back county flying  and a lot of times the landing area is not in the best possible shape. I would like to install 29" tundra tires on it. Due to the change in wheel and tire size do I need to get FAA permission to make the modification and if so what would be the process?

It's possible that a 337 exists as a one off approval.  Join the Piper forum to get that info.  If there is no 337, you probably need an STC which is something you can Google.

My initial thought is that it would be odd to use a low-wing for bush work. But I'm wrong, and there's a whole site about it: https://backcountrypilot.org/forum/bcp-low-wing-17587. My favorite quote from that page is "You don't need big tires, just big b#lls".

There is at least one PA-28 on floats as well.  It's a goofy looking plane.

Any time you make a modification to a certificated aircraft you need FAA approval. Even what appear to be minor things, like replacing you sun visors with better ones requires an STC. Putting in shoulder harnesses requires and STC. I could go on forever, but you get the idea.
Putting tundra tires on your Cherokee is a major change. If you look in the parts manual, your Cherokee probably came with 4 ply 6.00x6 tires so to change them you need an STC. You would also need to get an STC for the wheels and brakes. You’d probably need a new nosewheel fork as well.
I have never heard of anyone putting tundra tires on a Cherokee, but stranger things have happened.

STC is not the only option, there are also field approvals

I think @JScarry is correct.  This is not something you could do using a Form 337.  You would need a kit that includes a larger nose fork, and possibly longer axles, different brakes, etc.

@pericynthion I edited the answer. Technically you are correct that you can modify aircraft with a field approval, but a major modification like this would not qualify.

Why? 337s are major repairs or alterations.  Seems like with the right DAR and enough data, anything can be approved.

@acpilot I suppose you could put somewhat larger tires on a Cherokee with a field approval but if you are talking about real tundra tires—the ones that people like Trent Palmer and the Flying Cowboys use—I think it would be nearly impossible to get field approval. Maybe someone has done it. If so, I would love to hear how they did it.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
What is the name of the movement which is carried out by plane beginning from the runway and ending at takeoff?
What is the name of the movement which begins after the plane lines up on the runway and takeoff clearance is received, and ends when the plane lifts off from the runway? Is it also called as 'taxiing'? I know that roll-out is used for plane's decelerating movement on the runway after landing; but what is the name of vice-versa?

Related: What is a take off roll?

It's actually two things: Ground run until rotation starts, rotation until lift off.

Takeoff Roll
As per the FAA handbook (page 5-2)

Takeoff roll (ground roll) is the portion of the takeoff procedure
  during which the airplane is accelerated from a standstill to an
  airspeed that provides sufficient lift for it to become airborne.

And after that

Lift-off is when the wings are lifting the weight of the airplane
  off the surface. In most airplanes, this is the result of the pilot
  rotating the nose up to increase the angle of attack (AOA). >
The
  initial climb begins when the airplane leaves the surface and a climb
  pitch attitude has been established. Normally, it is considered
  complete when the airplane has reached a safe maneuvering altitude or
  an en route climb has been established.

I've been flying since the mid 70s and the term has always been "line up" as a generic term to describe the process of moving out onto the runway and stopping once aligned with the runway centre line.  As in, "when you line up prior to takeoff" when talking to a student.
When I was flying CRJs we would use the term "line up items" to describe pre-takeoff checklist items you do at the last minute while pulling out onto the runway (like selecting anti-ice, which had to be done as late as possible in the CRJ200 because its extremely hot evaporative WAI system would cook the deicing fluid on the ground).
As Carlo mentions, towers for all those years used the instruction "taxi to position and hold" until the change some years ago to "line up and wait".  It wasn't necessary to explain to pilots what that meant when the change happened.

The question is asking about the phase after entering the runway but before leaving the ground.

Yes but the question is not well worded.  He was actually asking if the takeoff roll itself was considered taxiing.   "Ending at the takeoff after the clearance", to Carlo and I, means a procedure that starts upon leaving the taxiway, before clearance is received, and ends at the start of the takeoff roll after the clearance is received.  That's the line up.  He should have just said, "is the rolling part of the takeoff still considered taxiing?"

This used to be known by ATC phraseology as ‘taxiing into position’.  I.e. were the aircraft is holding short of the runway safety area, ATC clearance for takeoff has been received, and the pilot release his brakes and taxis the aircraft into the runway safety area and lining up into a position to takeoff.  After a fatal accident, I believe between the DC-9 and a PC 12, this term was changed to ‘lining up’ ie “Line Up and Wait”

This would be correct if the question were about what happens on the taxiing landes. However, the question specifically asks about the runway.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
Can I land my aircraft on the grass next to the runway at a public airport?
The pavement is hard on my tires, so I prefer to land in the grass.

I've marked this as "too broad". This will depend massively on the airfield at which you are landing. How about you ask the operators of the airfield? Many will allow it and some will have specifically marked grass strips. Others won't allow it.

Welcome to Aviation.SE! As scotty says, as the question currently stands its impossible to answer this question as it will vary from airport to airport. I'd recommend you edit your question to specify the airport you're interested in and then if you haven't already done so, take our [tour] and check the [help] to see how this site works.

There are people on here who have been flying a long time and who can give reasonable informed answers for a question like this. It's not too broad at all.

I don't think it is "too broad". The question is tagged [faa-regulations], so it could be understood as What are the FAA requirements to be allowed to land on the grass on an airfield?

digging your wheels into a rut or hole in the ground is very hard on your gear struts and airframe... I'd not worry about the tyres too much, unless maybe you have those extra soft balloon tyres meant for snow and mud.

@Bianfable: the tag implies this is only being asked about the US, but the title doesn't say that.

@smci do you mean the OP should explicitly restrict the question to US regulation?

Why is the landing hard on your tyres?    They are consumable wear items and should serve a certain number of landing events before requiring replacement.  Are you not achieving the expected lifetime for the tyres?   Or do you land hard a lot or brake hard on landing?   Is there a runway you use a lot that is somehow extra harsh?

You seem to be putting an awful lot of stock on "in the grass".  Do you regularly land on farm fields, meadows, veldt, chaparral, and other lands not groundskept to be runways?

@Criggie I've heard it observed that grass landings have near-zero tire wear, but beat snot out of other components like oleostruts.

As someone who has done groundskeeping work before, I can attest that you can easily do thousands of dollars' worth of damage driving a heavy vehicle through a grassy area that has underground sprinklers.  Regardless of whether your plane can handle the terrain, please, please make sure that the terrain can handle your plane.  New tires can be cheaper than paying to have a half-mile of cracked irrigation pipe trenched up and re-run.

Possible duplicate of Can I land a plane in a field?

How do commenters not realize this is just a hypothetical... it's a fun question. Not to be taken too seriously. Surely OP does not intend to actually do this. Hence the joke about tires.

It depends on the airfield. Landing on grass is only recommended if the ground is maintained to a reasonable standard and clear of obstructions. Some airfields have grass strips maintained for that purpose, on others the grass has lights, wires and cables, or just lots of holes/ruts which will be far worse than the tarmac.
Some airfields are only grass, tarmac is not a prerequisite for having an airfield.
You want to know before you go, how to find out depends on where you are. There are flight guides and websites in many countries that tell you what is available, but it always makes sense to call ahead and ask the condition of the available grass, and to find out if there are any unofficial grass areas you can use.
There is also ATC, at a towered airfield you must land where you are cleared, you can'd decide to land on the grass nearby because you want to as it's a violation. If there's grass available you need to make sure you ask for it and they will give it to you if they can, most of the time ATC is helpful. If they say no there's probably a good reason. At an untowered airfield it's at your discretion, if there's grass available and it's in decent condition you would state your intention on the frequency and follow normal procedures.

In particular, since this question is tagged for FAA (i.e. U.S.) regulations, the chart supplement will give you information about the field, its runways, and, probably most important to this particular question, the contact information of the airport manager and/or owner, who you should definitely call before attempting something like this.

Some airfields are only grass, snow, sand or water indeed. A runway is a designated area, not a material.

A tongue in cheek reinforcement to the importance of confirming what's at the airport before heading to one, compare and contrast two airports in Victoria, BC, Canada - Victoria International (CYYJ), and Victoria Inner Harbor (CYWH). Both offer some overlap in services for small aircraft... But you probably shouldn't confuse the two if you're trying a Hail Mary instrument landing through fog...

Well, you're using land that is under the authority, or delegated authority, of somebody, so technically you need that authority's permission to use other than a designated landing area under the airport's license.  Remember that there could be liability issues for the person responsible for the airport, completely aside from the physical suitability of the area you want to use.
So from a strictly legal/regulatory perspective, you need the authorization of:
At a controlled airport, the delegated authority, ATC.
At a public uncontrolled airport, the delegated authority, the airport manager.
At a private airport, the owner.
In the real world, if you are using the grass at an uncontrolled public airport and you're not getting in anybody's way, you'll probably be fine, but if you land on the adjacent grass and then see a guy marching toward you with steam coming out of his ears, that's probably a manager or owner coming to chew you out because there is a policy against it.
Bottom line: the wise pilot checks with whomever is in charge first, if in doubt.

Also there's the little matter of the fact that the grassy area may well have obstructions that aren't visible from the air and aren't immediately obvious until they rip your undercarriage off at 100mph

What about landing on public land that doesn't fall under any of these categories, like a grass field in a public park?

It's up to the authority that is responsible for it.  There will likely be a by-law or some local ordinance preventing it use.


text:
How many flight hours do the first retiring A380s have?
I read news here that an A380 previously owned by Singapore Airlines has been decommissioned and scrapped. Another A380 from Air France was also retired. Others are nearing retirement as well. But it is not clear for me whether the retirement is due to the aircraft reaching the end of their design life or due to some other reason. If it is due to the design life, why are they still able to sell the scrapped parts (as done by the TARMAC)? Most comments I read are negative, which is sad.
Then my question, how many flight hours do these aircraft have? Is the retirement purely due to its design life being used up? Or for other reasons?

No they are nowhere near being worn out.  These aircraft are normally designed for anywhere from 40-60,000 cycle lifespans, and more on shorter haul a/c (depending on how long each cycle is), perhaps 30-40 years.  They are being retired and scrapped because they make no economic sense to run, and there is literally no used market for them, so the residual value of the airframes is the scrap value (the metal and the potential used spares value of all the bits attached to the metal, to the extent there is a spares market for them).
It's just an informed opinion, but I don't think Singapore (or its lessor) is in much pain over this.  An OEM trying to get market acceptance of a new type will often include residual value guarantees over some period of time.  I wouldn't be surprised at all to learn that owner is getting compensated by Airbus for the difference between the scrap value and some contractually guaranteed residual value of a 10 year old airframe, so they won't be the ones taking the hit; it'll be Airbus.
The problem was always one of adding a significantly larger type into a world designed for many many years around the 747 and all of its offspring.  Just too big.

The 747 has also hit the dustbin, along with airlines changing orders to the smaller a350-900 from the -1000 and the b77x selling poorly. 400 seats in these aircraft are too many, so 600 seats in the a380 are way too many.

Yeah it looks like 300+/- seats with two engines has settled in as the economic sweet spot for long haul.

SIA wont feel the pain as the lease of the aircraft has ended... the one feeling the pain would be the owner.. in this case I believe the Dr Peters group.

I wouldn't be surprised at all to learn that Singapore is getting compensated by Airbus for the difference between the scrap value and some contractually guaranteed residual value of a 10 year old airframe, so they won't be the ones taking the hit; it'll be Airbus. Are you saying that Airbus is buying the scrapped parts?

@AirCraftLover no, he is saying that the initial sale contract likely included a guarantee from Airbus about the residual value of the airframe after x years, so if they can only be sold as scrap that is worth less than the guaranteed value, Airbus would make up the difference.

@Pilothead 747s aren't selling well, but I think it's a bit much to say it "hit the dustbin" in the same vein as the A380. 10-year-old 747s aren't being scrapped for parts. They're still selling 747-8Fs. The 777X already has more orders than the A380 ever had and it's still over a year from entering service. The 777-8 is smaller than the 777-300ER and the latter is one of the best-selling wide-body airplanes ever made, if not the single best.

Sometimes what happens is the airplanes get to a point where they need to start adding reinforcements to the structure under Service Bulletins due to unforeseen cracking problems that came up in service or through long term fatigue testing.  An airframe sold as a 50000 cycle structure may need all kinds of patching at 35k in order to avoid onerous repeat inspections because of premature cracking or corrosion problems, and they may decide it's not worth the money.

In one word: ETOPS-240(-330/-370).

@reirab What used to be popular is not necessarily anymore, which is the point. Emirates downgraded 30 b777x orders into b787 and may cut more, Etihad wants to cancel 25, British has deferred some of its 18 firm, Lufthansa reduced 20 orders to options as it bought b787s. No US airline has ordered any. The b747 was not designed as a freighter and would not exist without the now cancelled passenger version. The smaller a350 and b787 are the popular widebodies now.

@Pilothead I would agree that the 787 (and probably also the A330neo [and hopefully eventually the NMA]) will have a larger market than the 777 going forward as point-to-point routes to medium markets grow, but I'd still say that the 777 isn't going anywhere any time soon. Hub-to-hub will definitely drop off some, but the 777 will still be the best choice for the routes between distant large cities. Markets like NYC, London, Paris, LA, Tokyo, Seoul, Beijing, and Shanghai will still require heavy metal going forward and other Asian markets will continue to grow.

The A380 that was being scrapped was the 3rd aircraft on the production line. After being used for a short time in the test fleet of Airbus, it became the first line number that was delivered to a customer. (Line No. 1 and 2 are still owned by Airbus).
The first few aircraft leaving a new production line are usually heavier and have different wiring than later builds, because the production process has not yet been optimised. For example, the wiring in early A380 fuselage sections was too short, so that after assembling the fuselage they couldn't connect the electronic cables. This led to rework that added weight and complexity.
Therefore, the first few aircraft from the production line have higher fuel burn (due to extra weight) and higher maintenance cost (due to the one-off quirks that are not found on later aircraft). This makes such aircraft uneconomic to operate and difficult to sell.
If it is hard to make money with such an aircraft anyway (the long-range market clearly prefers twin engine aircraft with approx 300-350 passengers), scrapping it will bring the most value.
The aircraft was not at the end of its technical design life. The design life of long range aircraft is in the order of 30-40 thousand cycles (flights). With two flights per day it would take approx 45 years to reach that limit. See also  What is the lifespan of commercial airframes (in general)?
I wouldn't be surprised if a few other A380s with low production line numbers will be scrapped in the next few years. However, in general I expect that the A380 will be operated for another 20+ years,  especially on high volume routes to airports with limited capacity.

I fail to see how you answer the first question ("Then my question, how long is its serving hours? "). I expected to see some estimate of flight hours or cycle numbers.

@Manu H design life of long range aircraft is in the order of 30-40 thousand cycles. With two flights per day it would take approx 45 years to reach that limit. See also  What is the lifespan of commercial airframes (in general)?

the question is not about lifetime in general but about this few early retired A380 specifically.

Air France's A380s aren't all that low on the production line - their newest one was delivered in 2014 - but they've already announced that they'll be retiring their entire A380 fleet within the next 3 years. So far, the secondary market for A380s has been exceptionally dry, so I'd be kind of surprised if they can find buyers who want to fly all 10 of them, unless maybe Emirates decides to buy them. Even that seems unlikely at this point, though.

@ManuH is correct. Your answer is out of focus, even it quite informative. As I said, it is not clear for me whether the retirement is due to the aircraft reaching the end of their design life or due to some other reason. If it is due to the design life, why are they still able to sell the scrapped parts?

The two A380s were scrapped by the Airbus should not be considered as scrapped product as they are still under development. We can not even say it as A380 as Airbus never declared them as number of their product. It is quite common for any company to canceled their design due to didn't meet expectation. But the thing of the A380 of ex-SIA is it was in service, but to short to be retired and scrapped. Didn't make sense.

@AirCraftLover the scrapped ex-SIA was the third A380 on the production line. Being an early build, it was heavy and non-standard, which makes it expensive / uneconomical to operate. For that reason it was scrapped. No other production models have been scrapped.

Many of the A380s due to be scrapped in the next few years are coming up on their first D-check (very heavy) maintenance, which is very expensive. They will also need their interiors updated, also quite expensive. Most airlines decided it just wasn't worth it to keep flying these things with these costly operations coming up, for an already economically marginal aircraft.

Related: How much does a D-check cost compared to a new aircraft?

I can well imagine that that's a main issue. Same with your old F250 -- you drive it, even if you'd actually only need a Subaru,  till the clutch goes, or until it needs new tires.


text:
On a flight with short stops, do you terminate flight following at each stop?
On a cross-country trip, is it normal to terminate FF at each stop and reacquire it (potentially just a few minutes later) for the next leg, or would ATC prefer that you advise them it'll be a short stop and maybe let you keep the code to reduce their hassle later?

Are you asking about landing at untowered airports? I've never had flight following continue through a stop, they always cancelled it once I said "airfield in sight" (which results in them saying "Roger N12345, radar services terminated, frequency change approved") and from then out you are not getting flight following anymore...

Yes, I was thinking of untowered airports, specifically for a student solo cross-country flight, where you're mandated to land twice but expect to be back in the air within a few minutes each time.

For my students, I have them leave the plane at each stop, get fuel, get a WX briefing, preflight again,  and file a new flight plan.  It gives them better practice at those things, which while they are not specifically flying, they are related.

Flight Following is intended to track your flight from time of activation to reaching your destination.  It provides for ATC services which include traffic advisories, and emergency services.  It is expected to terminate at point of landing.
That said, depending upon workload, some TRACONs will provide flight following which continues through approaches or even touch and goes at an intermediate airport.  However this is a workload and controller preference.  And it is not intended to support full stop landings, or passenger changes.  If you routinely make stops, you might let the controller know you will be back in 3 to 5 minutes, and they may keep your ticket alive, but that is only likely if they are not very busy at that time.
Flight following in Canada is called an en route radar service, which perhaps better describes flight following. In the US, years ago, a request was customarily made for "radar services" which were essentially that of flight following.
In summary, flight following is not intended to carry over "flight to flight" where flights are normally terminated by landings. Think of it as radar services, not necessarily a flight plan with SAR backup.

As @RonBeyer notes in the comments Flight Following will drop you when you land. Generally (also as Ron notes) they will ask you to call the "field in sight". It really depends on where you are and what kind of air space you are in. Where I fly in the Northeast they typically drop you when you have the field in sight but its hard to stray to far from a heavily controlled area if you are flying between DC and Boston but it may be different elsewhere.
Keep in mind that you will need to get off the frequency so you can make your CTAF announcements anyway. It may be a good idea to keep the controller as a listen only channel on COM2 if you are equipped for such in your aircraft.
Assigning you a code is not really a hassle for them so you don't need to worry. In a busy airspace ATC may want you out so they can handle IFR traffic. Remember flight following is "load dependent" so you might not always get it and you can be dropped out at any time.
When on your student XC's its always a good idea to preface one of your initial calls with "N123AB Student Pilot requesting flight following". ATC is there to help you and noting you are a student pilot may help you so they don't expect professional pilot level flying and radio chatter from you.

Thanks.  When I did my student solo xc long ago, my CFI was anti-GPS and anti-FF (dead reckoning only), so there was a lot I missed, and then I quit flying for over a decade.  The regulations haven't changed much, but I've got a lot of practical details to catch up on.

@Stephen Sprunk, perhaps you do not think so, but your CFI did you a great service.

If ATC is asking you to report the field in sight when you're VFR they're working too hard...


text:
Aerodynamic center vs center of pressure for guided MLRS
How to define static margin of guided artillery rocket with canard-free rotating tail configuration? In the E. Fleeman book, the aerodynamic center ($X_{ac}$) was used:
$ SM = {X_{ac}-X_{cg} \over d} $
But in other books about rockets, the term center of pressure ($X_{cp}$) was used:
$ SM = {X_{cp}-X_{cg} \over d} $
Which formula is correct for such canard-free rotating tail configuration?

Since rockets/missiles typically use symmetric airfoils and fuselages the aerodynamic center and the center of pressure are the same, because the zero-lift moment coefficient is zero.

But it is strange when i do some cfd simulations in Ansys Fluent at supersonic speed, the aerodynamic center and the center of pressure are not the same. The aerodynamic center is far forward the center of pressure. Note: Xac is calculated by ploting moment coefficient cm vs angle of attack and by finding the point at which moment coefficient is constant. Xcp is calculated by integrating static pressure over whole surface of the rocket.

Is your body not symmetric? Can you show a picture, or show us the curves and plots that indicate that aerodynamic center and center of pressure don't match?

The missile is axisymmetric with von karman nose, 4 canards on the nose and 6 tail fins freely rotating. The missile length is about 4.7 m, the Xac=1.98 m at M=3.5, the Xcp=2.4 m at  M=3.5 and AoA=0. The Xcp is calculated by intergrating static pressure over missile surface. The Xac is calculated by ploting Cm at various points along missile axial axis and find the point at which Cm=const.

I believe most texts are ignoring the contribution of the body and only including the wings -- or possibly even only looking at a single set of finds.  Fleeman's definition is correct.  Xcp is a useless quantity.  Drive it from your mind and never use it again.  Question any resource that uses it with suspicion.


text:
Can we use ECI coordinates for an airplane?
It is taught for navigation systems (like an airplane) on Earth we us ECEF (earth-centered, earth-fixed) and for space systems (like a satellite) we use ECI (earth-centered inertial). But why is ECEF exclusively used for navigation vehicles on Earth and ECI is exclusively used for satellites and spacecraft in space?  Why can't we use ECI for an airplane to observed another perspective?

You can convert between whatever systems you're interested in, but aside from some really trivial "gee-whiz" cases, there wouldn't seem to be any use for considering aircraft as flying in an ECI frame. Everything I'm flying in, around, over, and to are all pretty much "earth fixed" or close to it, so that's the useful frame of reference.

"Why can't we use ECI for an airplane to observed another perspective?" What do you believe would be gained for aircraft by using ECI rather than ECEF?

@CVn The airplane's Inertial Navigation box could be applied to ECI.

@Ralph I am just confused between ECEF and ECI.  I've memorized the theory, but why "earth-fixed?"  Looking for a clearer explanation.  If only using a gyroscope, then ECI would work better, right?

Because aircraft, though they leave the surface of the earth,  are "earth fixed", while spacecraft are not (see Voyager 1 & 2, Mars rovers, etc.). While you probably could apply ECI to them, it would probably be overkill.

Maybe someone can explain in layman's terms about ECEF and ECI and the convention of the types of navigational vehicles used for each frame.

The basic reason is the goal in navigation.  For an airplane it is to deliver the aircraft to a particular destination on the earth's surface, potentially also avoiding certain areas fixed to the earth's surface.
If you do all your navigation calculations in ECI, you then have to keep track of the earth's rotation to translate that to a point on the surface.  If you do all the navigation in ECEF, then that translation is unnecessary.
Both methods are mathematically valid (for ECEF, you have to have some method of removing or ignoring the non-inertial frame effects like Coriolis; for ECI, you have to keep track of earth rotation).  I don't have any direct evidence, but I suspect that since ECI was not an option historically, the current solutions are robust and no one is looking to create a radically different method for unknown benefit.

very few ECEF/ECI experts, thanks.

For ECI you not only have to deal with the rotation of the earth around its axis but its orbit around the sun (sidereal day vs. solar day).


text:
Flight physics for a roll
I am working on a pet project to write a game with flight physics. It will not be a simulator but instead much simpler.
What I have done so far
I have created winged components that generate lift and drag using the basic formulas I found online. I apologize if some of the debug info is not standard terminology.

The green arrows in the image show the force and magnitude begin applied. The yellow lines are the relative airflow.
What I cannot get working and understand
At first all the components used the same forward speed calculated by looking at the CG. Just an easy way to see what speed the plane was moving. The plane flew straight when "thrown" level and if will self correct if thrown with a slight roll angle.

The problem starts when each component starts calculating its individual forward speed. Even with dihedral applied to wings the plane will start rolling to the left more and more.

You can see that the left wing has a slightly higher AOA as the result of the dihedral. BUT it has a lower velocity than the right wing because the plane is yawing (I think). This lower velocity causes the right wing to produce more lift and the plane rolls more to the left. The more it rolls left the more the right wing speeds up causing it to produce even more lift.
I have tired to increase the rudder, but that didnt help at all. Removing the rudder causes the plane to over correct, and then to roll to the left too.
Can any body explain what is suppose to happen when a plane rolls.
From what I see the plane rolls left, it pitches slightly down. The right wing "swings" forward faster than the left causing more lift.....

It's not completely clear if you are trying to model an intentional pilot-commanded roll -- like a complete aileron roll? --  or how the plane reacts if a bit of turbulence puts it into an unwanted bank angle the pilot does nothing to correct. In the latter case it's not really a "roll" that you are trying to model-- I'm trying to think what would be a clearer terminology--

I apologize, i see what you mean. This is without any pilot input at all at this stage. Its basically a model plane begin "thrown" and it was not completely level at that moment . There is no turbulence or any forces acting on the plane except lift, gravity and drag. Imagine one of those 2 part balsa planes where you slide the wing into a slot in the body. You throw it, but the wings are at a 45' angle. The plane starts leveling out right after you launched it. My question is why does it level out, I am not seeing that in my model as the outside wing generates more lift.

The problem I was facing  is known as Spiral Stability and it seems the dihedral and rudder surface area play the biggest rolls.  http://www.rc-soar.com/tech/spiral.htm

Typical airplane is not stable in roll. The outside wing flies a bit faster, which does indeed make it produce a bit more lift and that in turn will make it bank into the turn, tightening it and if left uncorrected, ending in a spiral dive.
In a coordinated turn, an aircraft even can't be made stable in roll. There is no way to create a restoring force without involving side-slip.
The only thing that can be provides is the yaw-roll coupling where a slip produced a rolling moment into the slipping turn. This rolling moment is affected by dihedral and sweep.
Fortunately as the turn tightens, if the rudder is held fixed, some slip does develop that can provide the restoring force reducing the bank. However, it causes another dynamic mode, the Dutch roll.
As the bank increases, the tendency changes from Dutch roll to spiral mode. If you wanted to avoid the spiral mode, the Dutch roll would be very strong, so practical aircraft are designed with moderate yaw-roll coupling and do require a bit of opposite aileron in turns.

I see exactly what you described. The plane at the moment does continue into a spiral dive. My only flying (I have done myself), has been with model airplanes. I was expecting it to behave in the same manner. If you look at a typical "first RC plane" like a Gentle Lady Gilder that does not have ailerons, but only rudder and elevator controls, what causes this model to self correct on a roll ? Lets say you aggressively used the rudder that caused the plane to yaw and roll and you center the rudder again.  Why would that not also continue into a spiral roll ?

@CharlCillie, it probably has quite strong yaw-roll coupling. Still I would think it would continue in a spiral dive if you made a sufficiently sharp turn and only centered the rudder instead of using opposite input to end the turn.

"In a coordinated turn, an aircraft even can't be made stable in roll. There is no way to create a restoring force without involving side-slip " -- this is an important statement for all amateur enthusiasts of stability and control dynamics to understand.

Your question is challenging to understand quickly, let alone answer well.  For starters, what exactly are you doing with dihedral?  Do you understand how the roll torque created by dihedral, in any given situation, is entirely due to sideslip, and the resulting way that the sideways airflow "sees" each wing at a different angle-of-attack?
If not, that's one thing that would need to be fixed before you can continue with this. If you want your "model" plane to automatically tend to slowly roll back toward level in the absence of aileron deflection, you are going to have to model how banked, turning flight involves a curving flight path, which means that there is a curving aspect to the relative wind, which tends to make the vertical fin "feel" a sideways airflow, which generates a yaw torque that displaces the nose toward the outside of the turn, exposing the wing to a sideways airflow.  Like this: https://www.av8n.com/how/htm/yaw.html#sec-long-tail-slip  .  It's not sufficient to imagine that the plane just tends to "fall" toward the low wingtip whenever it banks-- that's not really what drives the slip. It's all about the curving flow.  And it's certainly not correct to imagine that the dihedral (or the high wing placement) will create ANY self-leveling tendency at all, in the absence of slip (sideways flow).
So basically there's so much going on here that you may need to ask about ten different questions to even start to "unpack" how your computer model needs to be improved.  A good start would be to peruse this website and play close attention to all sections that deal with yaw stability, roll stability, sideslip, roll control, etc -- https://www.av8n.com/how/
It's normal for an aircraft with only modest dihedral to tend to wind up into a steeper bank angle, but if you aren't accurately modeling the stabilizing effects of dihedral, as I'm guessing may be the case, you'll end up over-estimating this tendency for the bank angle to increase on it's own.
I'd encourage you to try to think of some more narrow, individual questions to ask to help you "unpack" your problem some more.

Imagine if you can the days before remote controls where "toy" planes would only have a motor that would pull it up into the air in a slow spiral. No pilot input. The motor would run out of fuel and the model would glide down. I expected dihedral would be the main reason for the plane not to roll over. I do see that the the lower wing has a bigger AOA and it makes sense. The problem is that the upper wing has a higher air flow speed, causing it to have more lift. Instead of correcting the plane it rolls it more. I am trying to understand why the real world one does not roll over too.

Thank you for your reply and links. They are a pot of gold to me. I will work on exactly on what I am trying to find out and after going reading all the info you linked to, get back.

It's true what you say about the higher wing, the wing on the outside of the turn, having a higher airspeed. It's also true what you say about the lower wing having a higher angle-of-attack due to to dihedral, in the presence of a sideways flow toward the high wingtip, but the question of exactly what is causing the sideways flow is not a simple one.  It's not really adequate to imagine that the aircraft is simply "falling":toward the low wingtip.  Anyway, I see that you are on the right track in some ways in terms of trying to think critically about some of these issues.

Thank you for taking the time to share your knowledge. I am going to dig in and find why I am not seeing the results I expect and share it here.


text:
How do you maximize an electric engine's thrust?
I've been recently looking for answers to this question on the internet but the jungle of propellers, fans and electric motors didn't quite get me an answer.
How would I have to design an electric engine to produce as much thrust as possible on an area as small as possible, so the thrust/area ratio should be high. Also, assume there's enough power available.
Would I use propeller and if so, how many blades?
Would I use a fan like the turbofan of a jet engine?
With the optimal solution, which thrust do you think a 500 mm prop/fan could produce?

Thrust-to-area ratio is an odd figure - why do you want to optimise for that? If power is not an issue, one would probably make an extremely long series of increasingly complex compressors to accelerate pretty much indefinitely, so perhaps you want to add some more constraints to your question as well (most likely: single or double stage compressor/fan/propeller)

Why use propeller? Use a compressor, e.g. driving the compressor stages using a electric motor, and jet the high pressure stream.

@Simon Henn it would help a lot to specify your target flying speed.  Unless it is greater than around 450 mph, find a way to put a prop on there.  Multiblade props or fans will drain your battery much faster for a given amount of thrust.  Ducts are more efficient than open props only at lower speeds, losing efficiency in comparison at higher speeds due to drag.

Generally, if you want to optimize for area/diameter (without the complexity and weight of the many/multi stage option mentioned in comments to the question), you'll want to use a ducted fan (roughly similar to the fan on a turbofan).  Not only do you avoid tip losses due to the end plate effect of the duct (if the clearance isn't excessive), you can run the fan at arbitrarily high speed, even with supersonic tips, without the extreme drag and noise production of an open propeller in such a regime.
Look at the design of EDF (Electric Ducted Fan) engines used to simulate jets in small radio control models; some of these can product thrust comparable to fans driven by high performance methanol/nitromethane glow engines (15-25 kW/L displacement, with 10 cc, 1.5 kW engines driving fans 15 cm diameter), with 10-20 minute flight duration on a charge with light enough batteries to fly well.  Scaling these up to 500 mm diameter will generally require shortening the blade chord relative to diameter, and you'll need to optimize pitch for the combination of rotation speed and torque available.

Noise yes, but the wave drag will still be all there if you run supersonic. It is still never advisable to have supersonic tips.


text:
On an IFR flight, should I avoid class B and include approach fixes/procedures in the route?
When creating an IFR route, should one route around and avoid class B airspace?  Should one include the IAF (Initial Approach Fix) of the desired IAP (Instrument approach Procedure) in your route?  Should one include the desired STAR and/or SID in the comment section or route section?

Welcome to aviation.SE! Are you asking about the US, or another country?

You don't need to.  If enter a start & end point at https://skyvector.com/, it can suggest standard routings for you.  You can follow those, or tweak it up some.
For example, 6B6 to WWD, standard routing will put you on V1 and will take you out over the water quite a ways, farther than I prefer to be in my single engine 4 seater. I'd tweak that to route over JFK, Colts Neck VOR, Atlantic City instead, having been cleared for that route several times by NYC approach. IFR at 6000, and VFR even, at 6500 feet.
I've also talked to pilots going north & eastbound who were IFR and routed north around the NYC Class B, sometimes quite a few miles out of the way. So it really depends on what the weather is doing and how busy the Class B is at the time of your transition.
For the approach part, I'd leave that out as conditions can change and your approach will be determined by the weather at the landing end and ATC will assign what to use as you get closer, or you can request a Visual Approach if the weather is nice and you don't need the approach. One thing you can do is put "No SID, No STAR" in your flight plan if you don't have them on hand.


text:
If airports with pilot controlled lighting share a CTAF frequency, could the lights be triggered at multiple airports?
In the US, CTAF frequencies can be shared between several uncontrolled airports.  That is, a pilot around airport A can hear the transmit of another pilot utilizing airport B.  The question is can a pilot using the shared CTAF frequency and clicking the Pilot Controlled Lighting (PCL) affect the lights of all nearby airports using that same CTAF?

In theory, this could happen.  The consequences may not be severe - wasted power, some light pollution, and a false impression from seeing the lights alone that an(other) aircraft is trying to use the airport when in fact it isn't.
However, it may be less likely than you think.
For one, an aircraft in the air, even at pattern altitude, is going to have a much better path of radio propagation to another aircraft in the air, than an aircraft over one airport may have to a ground antenna at another - in simplistic terms, the radio horizon has doubled.  Ideally (for example in planning towers for a cellular phone network) frequencies are not re-used within the range of expected propagation, but only beyond it - however, in the aircraft-to-aircraft case you have doubled that over the air-to-ground case.
For another, an aircraft receiver is designed to be able to pick up weak signals.  In contrast, the receiver and decider for pilot controlled lighting may have an intentionally high signal threshold, to only trigger on strong nearby transmissions, and not on distant ones, random radio noise, or weak harmonic interference from transmitters on non-aviation bands or unintended emissions from non-radio equipment.


text:
Why is the N-number on the tail of aircraft sometimes shown in both large and small font?
Why is the N-number on the tail of aircraft shown again much smaller and above the main N-number? They are both the same group of letters and numbers.

Welcome to aviation.SE! Although your description is clear, a picture would be very helpful here, if you have one (or can find one).

I'm not sure why the N number would be repeated, but in trying to find out I discovered there are a lot more marking requirements than I would have thought

It isn't like that on my aircraft.

The N-Number marking regulations are outlined in this AC for fixed wing aircraft:

... minimum height of 12 inches
(1) On both surfaces of a single vertical tail or on the outer
  surfaces of a multi-vertical tail, or
(2) On the fuselage surfaces, on
  both sides of the fuselage between the trailing edge of the wing and
  the leading edge of the horizontal stabilizer. If engine pods or other
  equipment are located in this area and are an integral part of the
  fuselage side surfaces, you may place the marks on those pods or
  equipment.

However for some time 2 inch markings were allowed:

On an aircraft displaying 2-inch marks before November 1, 1981, and on
  aircraft manufactured between November 2, 1981, and January 1, 1983,
  you may display those marks until the aircraft is repainted or the
  marks are repainted, restored, or changed. Once the aircraft is
  repainted or the marks are repainted, restored, or changed, the
  N-number is required to be 12 inches high.

Its possible the numbers you are seeing are the old ones and the new 12 inch numbers were applied directly beneath it to comply with the new marking regulations while the old ones were simply not removed.

I did read the marking regulations. However, when they mentioned the 2inch markings I didn't think that the second N-number could be an old to-be-removed marking. Thanks for pointing that out.


text:
Why does the diffuser section generate thrust in a jet engine?
I am studying the thrust distribution of jet engines.
But I'm now a bit confused.
In Rolls-Royce's "The Jet Engine" book,

http://aeromodelbasic.blogspot.com/2012/05/thrust-distribution-distribution-of.html

At the start of the cycle, air is induced into the engine and is compressed. The rearward accelera- tions through the compressor stages and the resultant pressure rise produces a large reactive force in a forward direction. On the next stage of its journey the air passes through the diffuser where it  exerts a small reactive force, also in a forward direction

I understand the first part of the paragraph that the compressor is providing forward thrust, as it is pushing (so compressing) air rearward. But why is the diffuser also providing forward thrust?
And also why the nozzle is providing rearward thrust?
The similar conculsion is also shown here:
http://www.pulse-jets.com/phpbb3/viewtopic.php?t=2183, that the diffuser is providing positive thrust by calculating the pressure force.
From my understanding of basic fluid mechanics,
shouldn't a nozzle be providing forward thrust, like the sprinkler in the garden or a fire hose?
And shouldn't a diffuser be providing rearward thrust, as the outlet speed is slower than the inlet speed, and so m dot X (v - u) is negative?
What's wrong with my understanding?

Is the text you are quoting the text from RR's book, or text written by the person who posted the picture on the blog site you link to? Your understanding seems perfectly fine to me, I would like to verify the context of the diagram.

It's from RR,
See P.218 Paragraph 3 in https://docs.google.com/file/d/0Bx0MqOfev7dnS01DMmtqSmhoVmc/edit

because the inner surface of the nozzle faces front so the gas pressure pushes it back, very simple.

But why is the diffuser also providing forward thrust?

The diffuser slows down the flow to ease fuel-air mixing and combustion a bit later. If you only focus on entry and exit speeds, there would be no thrust.
However, if you look at the pressures on the diffuser walls, a different result emerges. Slower flow means higher static pressure, and the total pressure right at the compressor exit is already the highest within the whole engine. The pressure on those widening diffusor walls does indeed push the engine forward because of the forward slant of the pressure vector (which acts perpendicularly to the diffusor walls). Your linked pulse jet page explains this quite well.
Of course, no thrust would result if the flow were not heated and thus accelerated further downstream. So the diffuser all by itself will not create thrust; this happens only when it is placed inside a working jet engine.

And also why the nozzle is providing rearward thrust?

This is not always the case, but here the nozzle has a converging shape which helps to accelerate the subsonic flow and converts the remaining pressure to speed. The walls now have a backward-facing slant, so the pressure vector on them will contribute a backward-facing component. In addition, the high flow speed along the large nozzle walls causes some friction, which needs to be considered, too.
For a comparison, look at the cone behind the turbine wheels. Its thrust contribution only stems from the forward-facing pressure acting on it.

But can you explain why don't i need to consider the pressure difference when i am calculating the thrust of a fire hose or garden sprinkler, but i need to consider the pressure difference when i am calculating the thrust contribution of a nozzle or diffuser? What makes them so different?

@Jono: What makes you think that you should not consider the pressures in garden hoses? What makes them different???

It seems like the engine nozzle and garden hose nozzle have a lot of similarities to me. Garden hose: 1. High pressure created by water pump/tap at inlet; 2. Low pressure at outlet (atmospheric?) 3.Water accelerates from inlet to outlet.. and Engine: 1. High pressure created by compressor/ombustor/turbine at inlet, 2. Low pressure at outlet (atmospheric?) 3. Air accelerates from inlet to outlet... But why is the nozzle in engine creating thrust in the same direction as the fluid flow (to the right as the picture above), while the garden hose is creating thrust in the opposite direction?

And shouldn't a diffuser be providing rearward thrust, as the outlet speed is slower than the inlet speed, and so $\dot{m}\times(v - u)$ is negative?

Conservation laws in physics are an excellent tool. They let you calculate a lot without looking at the minutiae details of the actual process. And this is great example: you can trivially calculate thrust of the whole engine from the change of momentum of the working fluid. But that won't tell you how the force is actually applied, only the sum of the forces on the entire engine.
The thrust break-down is the minutiae details of the process. And at that level, the only way to create a force is by pressure of the fluid, and since pressure always acts perpendicular to the surface, only the aft-facing surfaces can have forward thrust act on them, while any forward-facing surfaces have negative thrust act on them.
And it's no different in the sprinkler. The pressure inside is acting on all the walls, but there is a bit missing in the nozzle where the water flows out, so the force on the opposite wall prevails.

,I also think that diffuser produce rearward thrust,because walls from diffuser are facing backwards and pressure allways act  prependicular to the surface..


text:
Why is the time of useful consciousness only seconds at high altitudes, when I can hold my breath much longer at ground level?
This answer says at FL500 (50,000 ft; 15,250 m) the time of useful consciousness is only 6 to 9 seconds.
But if I just stop breathing at any arbitrary time, without any preparation, I can easily continue without air for about 20 seconds. How can these times be so short?

It's worth noting that the time of "useful consciousness" is much shorter than the time of "consciousness", because the effects that appear in the situation make the consciousness much less useful to solve practical problems: Tunnel vision and euphoria may be very distracting, while still being conscious.

I the graphics and details in this answer - when you are fully exhaled at sea level, you have more leftover air in your lungs than you have when you are fully inhaled up at that altitude.

When you are breathing, oxygen ($\mathrm{O}_2$) and carbon dioxide ($\mathrm{CO}_2$) are exchanged between the alveoli in your lungs and the environment. This gas exchange is based on diffusion, which means the partial pressures of each gas involved will move towards equalization:

Henry’s law states that the amount of a specific gas that dissolves in a liquid is a function of its partial pressure. The greater the partial pressure of a gas, the more of that gas will dissolve in a liquid, as the gas moves toward equilibrium.

(source)
As long as the oxygen partial pressure is higher in the environment, your blood will gain oxygen from breathing. But if the oxygen partial pressure is lower, you lose oxygen from breathing. Therefore, holding your breath at sea level gives you more time until you run out of oxygen than breathing at 15km altitude, where total pressure is about 10 times lower than at sea level. Furthermore, as John K pointed out in the comments, holding your breath at sea level allows you to feel when you need to breathe again, because of increasing $\mathrm{CO}_2$ levels, where breathing at high altitude does not feel different because $\mathrm{CO}_2$ can still leave your system.
This principle also allows oxygen masks in aircraft to function without creating higher pressure. Since (more or less) pure oxygen is created, the oxygen partial pressure is much higher than in the surrounding air despite being at the same total pressure.

So if you could hold your breath, you could stay conscious for a minute or so as normal, but attempting to breath no only removes the remaining oxygen from your lungs, but also removes oxygen from your blood?

@RobinBennett In principle yes. But note that during a rapid depressurization you cannot really hold your breath. The air will be forced out of your lungs anyway. Holding your breath at sea level pressure gives you the "minute or so". I clarified the answer.

Other thing is that when holding your breath on the ground what forces you to breath again is the carbon dioxide buildup in your blood, not the lack of oxygen. If it wasn't for that, you could easily make yourself pass out. When cabin pressure is reduced slowly, you won't even be aware of the pressure drop because you are still able to expel CO2. When I took a High Altitude Indoctrination chamber ride back in the 80s, the biggest surprise when I started breathing 25000 ft ambient air was I couldn't tell the difference, just sitting still in my chamber seat, until the hypoxia symptoms set in.

@JohnK Good point, I added it to the answer.

We recently had a question about an ATC controller suffering from a stroke while on duty. Some of the commenters to the original YT video said they had a stroke themselves and didn't notice either. I suppose it is the same with that low-oxygen situation: You just don't notice yourself and that makes it so dangerous.

@JohnK's point about CO2 levels being important is also relevant at sea level or even below. There's quite a lot of information about this reflex as purging the body of CO2 is a cause of drowning in freediving

@PerlDuck the biggest problem is that for many people the initial hypoxia symptom is the euphoria stage, which is very similar to being on laughing gas at the dentist.  My initial symptom, luckily for me, was tunnel vision. Meanwhile a seatmate went straight to euphoria and was cackling in laughter as he tried to draw his shapes.  I reconnected when I felt a weird dunk sensation well up as I observed my tunnel vision, then all the symptoms vanished.  You're sitting drawing characters on a clip board. As your characters become all lop sided, you are AWARE that they are lopsided, but don't care.

@RobinBennett correct, but (as you may know but isn't pointed out in the answer yet) you can't hold your breath through a decompression event even if you know it's coming. It's not possible to sustain a significant pressure differential between the inside of your lungs and the cabin. The air will get out, probably doing some damage along the way if you try to keep your nose and mouth shut.

This is essentially the same reason why hyperventilating before diving is so dangerous: it reduces your CO2 without affecting O2, so it suppresses your need to breathe, potentially until it's too late.

@RobinBennett : The problem is that when the pressure drops, your body won't shut down your breathing automatically. There is no reason to, because our ancestors never encountered such problems. By the time you consciously realize what happened, you already breathed out the precious contents of your lungs. On the other hand, if you fall into water, your body stops the breathing automatically and instantly (as our ancestors often faced such situations).

@Bianfable Yes you can, and it's lethal. In scuba diving, there's a standard technique called CESA (controlled emergency swimming ascent) where if your air fails and your buddy mysteriously vanishes, you swim up to the surface. You're trained to do a controlled exhale throughout the ascent, because if you hold your breath then the gas expands as the water pressure reduces, and it can fatally rupture your lungs.

@JohnK: you can cause yourself to pass out from lack of O2 if you hyperventilate first, because it lowers your blood CO2, and it can be very dangerous: https://en.wikipedia.org/wiki/Freediving_blackout#Shallow_water_blackout

The situation in a high altitude depressurization is different because:

The air in your lungs is now "FL500 air" - i.e. the pressure is about 0.1 atmosphere. This means that the partial pressure of O2 (ppO2) is about 0.021 atm, instead of 0.21 atm. Oxygen will rapidly diffuse out of your blood and into your lungs, and your brain will very soon not have enough oxygen to function. (You can actually manage with a slightly lower partial pressure of O2 - scuba diving mixes are often considered "hypoxic" once they're below 16% O2, since your can breath a ppO2 of 0.16 atm and function normally. But note that this is 8 times greater than 0.02 atm).
You cannot hold your last breath of cabin pressure air. To try do so would in fact be very dangerous, since your lungs would be trying to support a 0.9 atm pressure difference between the inside and outside. Scuba divers are taught to never hold their breath while ascending for exactly this reason - the pressure difference can rupture the alveoli in your the lung. This can result in gas passing directly into the blood and causing an embolism.
But if you stick on an oxygen mask, that 0.1 atm of air (with a ppO2 of 0.02) has been replaced by 0.1 atm of O2. So your ppO2 is then 0.1. Still not ideal, but much better than 0.02 atm.

If you're wearing an oxygen mask at FL500, it's going to be a pressure-demand mask (which feeds oxygen to your lungs at higher-than-ambient pressure), providing your lungs with a ppO2 of 0.16-0.2 atm (this leaves your lungs holding a small pressure differential - 0.06-0.1 atm in our example, potentially up to 0.18-0.2 atm at higher altitudes - but they handle small pressure differentials like these without much trouble).

0.16atm ppO2 allows functioning normally if you're not exerting too much.  You'll probably feel it if you try to run up a flight of stairs, or cycle over mountain passes (I've done both at around that pressure)

Ok so the idea is that the pressure in the bloodstream is controlled by the external air or water pressure, while the pressure of the gas in the alveoli can be raised well above the external air or water pressure by holding one's breath during decompression or rapid ascent--

At FL500 your mask doesn't work very well.

@quietflyer I don't think I'd use the phrasing "well above" in that context.  Alveoli start to rupture and create air emboli at very little above 0.2 atm, and it takes conscious effort to exhale at much lower pressure difference than that -- making just breathing a tiring task over a fairly short term.  Most people cannot exhale at all against 0.2 atm.

It's also the starting gun.
When you hold your breath, you choose when to start.  That is known.
In a hypoxia incident, you rarely discover the pressurization problem at the very start of the event. It may be well along before you notice it.   So you don't know when you actually started "holding your breath".
It would be more of a fair comparison if the failing system went "loss of cabin pressure in 3, 2, 1...” But of course, it doesn't do that!